Socket kits or sets usually have a ratchet wrench, various adapters, accessories or attachments, and a plurality of sockets used interchangeably with the ratchet wrench. The ratchet wrench comprises a driving handle having a square-drive tang or stud which, for example, may constitute a 1/4", 3/8" or 1/2" drive. The sockets usually have an output hexagonal bore for engagement with a nut or head of a bolt; and these hexagonal sockets may range, for example, from 3/16" to 3/4" in sixteenth inch increments.
The average ratchet wrench kit may have about a dozen individual sockets, each of which is stamped with the size of its output hexagonal bore. These size indications are hard to see, especially when used beneath a vehicle, in cramped quarters, or in poorly lighted working areas. The individual pieces in a kit sometimes get mixed up, and the problem may be compounded due to English and Metric sizes.